running off

Hi our 6 year old son has adhd and has recently started running off when upset. I am getting frightened to go anywhere because of this behaviour. He had a meltdown a couple of weeks ago because I would not go into a shop (he wanted something, I said no) and after 20 minutes I ended up attempting to carry him home. He broke free and ran accross a road, twice. A neighbour came out to help and I dread to think what would have happened if she had not got him back onto the pavement. Then last weekend he thought that it was a game to run off and hide in a DIY store. Yesterday after school, the ice cream van was not there so he ran down a genel, climbed over some unsafe wooden fencing into someones front garden. He then leant over the fence looking at me and spitting. When we got home he grabbed a bag of cereal and poured it all over the living room carpet and stamped it in, then threw toys at the back of my head and kicked the radiator hard. He got frustrated reading last night and started scratching my husband who was sat next to him.I am constantly anxious and dreading the weekend again. The childrens centre nurse has advised me not to get emotional in front of him but he frightens me with his dangerous behaviour and I end up in tears from fear and frustration.